Specific examples of internal combustion, especially exhaust gas catalysts for an automobile engine include the following: ternary catalysts that simultaneously process carbon hydride, carbon monoxide and nitrogen oxide (NOx) in the exhaust gas; oxide catalysts that simultaneously process carbon hydride (HC) and carbon monoxide (CO) in the exhaust gas; NOx storage reduction catalysts that store NOx in the exhaust gas when an air-fuel ratio is in a lean state, and reduce & process NOx by switching the air-fuel ratio to a theoretical air fuel ratio or rich state before this NOx becomes saturated; and NOx selective reduction catalysts that reduce & process NOx in the exhaust gas by a reducing agent.
The ternary catalysts, the oxide catalysts, the NOx storage reduction catalysts and the NOx selective reduction catalysts are produced by coating a slurry form of catalytic components in these catalysts to a ceramic honeycomb form support and by sintering this, respectively.
However, because catalytic components are uniformly formed in a support in the most of the conventional exhaust gas catalysts, when the exhaust gas inflows into the exhaust gas catalyst, the gas diffusion speed of the exhaust gas is slow, and as a result, it would often appear that the exhaust gas is not sufficiently processed. Further, in association with the increase in the exhaust gas temperature, heat resistance that is required for the exhaust gas catalyst is increased. However, in the conventional composite oxide, the heat resistance is insufficient and it would often appear that the catalyst performance after the heat treatment could not be sufficiently maintained.
In the meantime, in Japanese Patent Application Laid-Open No. 2002-191988 (Patent Literature 1) and Japanese Patent Application Laid-Open No. 2002-253968 (Patent Literature 2), an NOx storage reduction catalyst where the gas diffuseness of the exhaust gas is enhancement and clarifying efficiency of NOx is improved by supporting noble metal and NOx storing agent to the coating layer made from a porous structure where fine pores having a specific pore diameter are established is proposed. However, in the exhaust gas catalysts, enhancement of the gas diffuseness of the exhaust gas in the layer of the catalytic component and improvement of processing efficiency of the exhaust gas are still in demand.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2002-191988
Patent Literature 2: Japanese Patent Application Laid-Open No. 2002-253968